On 4/1/2008, Charles Blackham wrote:
Does anyone have any experience of providing useful lightning protection for outdoor mounted equipment under these conditions? Hi Charles: I have some experience with telecom installations where the ground connection to the primary protector for a twisted copper pair is disconnected. That scenario occurs more often than many people realize. However, due to way that the wireline PSTN is constructed, there is a "reasonable" upper bound on induced (not direct) lightning surges of about 5 KV. So, if a manufacturer wants their equipment to survive whether or not the primary protector is functioning, the equipment can simply be designed to withstand 5 KV on the wireline ports. You don't provide many details on the equipment you are working with, so it is hard to comment on your options for an ungrounded protection strategy. The main benefit of having a hard wired protective ground is to ensure that the lightning return current takes a known, safe path to ground instead of an unpredictable path that travels through sensitive circuitry. If the equipment does not contain a path to ground, it will not attract lightning return currents in the first place. So, if there is a way to make the equipment fully isolated from ground up to the level of induced surges that you expect, you can protect the equipment that way. Joe Randolph Telecom Design Consultant Randolph Telecom, Inc. 781-721-2848 (USA) [email protected] http://www.randolph-telecom.com <http://www.randolph-telecom.com/> - ---------------------------------------------------------------- This message is from the IEEE Product Safety Engineering Society emc-pstc discussion list. Website: http://www.ieee-pses.org/ To post a message to the list, send your e-mail to [email protected] Instructions: http://listserv.ieee.org/request/user-guide.html List rules: http://www.ieee-pses.org/listrules.html For help, send mail to the list administrators: Scott Douglas [email protected] Mike Cantwell [email protected] For policy questions, send mail to: Jim Bacher: [email protected] David Heald: [email protected] All emc-pstc postings are archived and searchable on the web at: http://www.ieeecommunities.org/emc-pstc
